Sen. Dianne Feinstein said in an impassioned floor speech Wednesday that the Assad regime has the capacity to kill “tens of thousands” with chemical weapons, saying, “If the world doesn’t respond now, we bear responsibility for a larger tragedy happening later.”

Feinstein said if diplomatic efforts to disarm Syria of its chemical weapons fail, “I know we’re going to be back here on the floor” debating a war resolution for a military strike.

The California Democrat who chairs the Senate Intelligence Committee strongly backs a U.S. military intervention.

Feinstein said she met with the Russian ambassador this week, who described Russia’s intention to get Syria to disarm. “It was sincere,” Feinstein said. “The ball is really in Russia’s court. Russia is taking the lead in this. I trust it is sincere. I trust that the United States and Russia will come together and that it will be possible for the United Nations to act so the U.S. won’t have to.”

She said she was most affected by a video of a Syrian girl with long dark hair, wearing pajamas, who “looked just like my daughter” at that age, except that she was dead from a gas attack.

Feinstein described in graphic detail the effects on victims: “Foaming mouths, pinpointed, constricted pupils, the signature of sarin gas, convulsions, gasping for breath, all happening as the nervous system begins to shut down,” as well as “rows and rows of bodies” at an improvised morgue.

Feinstein emphasized the intelligence, which she said could not be released fully without compromising sources, that provided what she said is incontrovertible evidence that the Assad regime used chemical weapons. She said initial attacks were small, killing eight to 10, people, and that that Aug. 21 attack that killed an estimated 1,400 or so was a major escalation.

She cited Hitler’s use of gas in the Holocaust, millions of casualties from chemical weapons in World War I, saying that allowing the Syrian attacks to go unpunished would invite more attacks from Syria, and encourage use of such weapons by North Korea, whose arsenal dwarf’s Syria’s, she said, and threatens 28,000 U.S. soldiers based across the border in South Korea.

“If nothing is done to stop this use (chemical weapons) will be used in future conflicts,” Feinstein said. “I am really sure of that.”

She said she is certain that Assad, “will use them again. They are ready to go. Why would Assad load bombs with chemical weapons and not use them?”

Feinstein said not acting would send “such a signal of weakness to the rest of world, that yes, we are a paper tiger. That’s going to be conclusion in Iran and North Korea.”

She quoted Albert Einstein, who famously said, “The world is a dangerous place to live, not because of people who are evil but because of the people who don’t do anything about it.”

She pleaded with the public not to allow the United States to give up its “leading role in the world. We are the nation that others look upon to stop repressive dictators and massive violations of human rights,” she said. “We cannot withdraw in our own borders and do nothing and let the world do nothing.”